The element that serves as the modal container has a role of dialog.
All elements required to operate the dialog are descendants of the element that has role dialog.
The dialog container element has aria-modal set to true.
The dialog has either:
A value set for the aria-labelledby property that refers to a visible dialog title.
A label specified by aria-label.
When a dialog opens, focus moves to an element inside the dialog and depends on the nature and size of the content (usually the header element).
If content is large enough that focusing the first interactive element could cause the beginning of content to scroll out of view, it is advisable to add tabindex=-1 to a static element at the top of the modal, such as the modal header or first paragraph.
If a dialog contains the final step in a process that is not easily reversible, such as deleting data or completing a financial transaction, it may be advisable to set focus on the least destructive action, especially if undoing the action is difficult or impossible.
If a dialog is limited to interactions that either provide additional information or continue processing, it may be advisable to set focus to the element that is likely to be most frequently used, such as an OK or Continue button.
When a dialog closes, focus returns to the element that invoked the dialog unless either:
The invoking element no longer exists. Then, focus is set on another element that provides logical workflow.
The workflow design includes the following conditions that can occasionally make focusing a different element a more logical choice:
It is very unlikely users need to immediately re-invoke the dialog.
The task completed in the dialog is directly related to a subsequent step in the workflow.
